Reversible and irreversible thermo plastic bonded abrasive articles



?atented Oct. 6, 1931 UNITED STATES PATENT OFFICE RAYMOND C. BENN'ER, OF NIAGARA FALLS, AND GARNET! H. PORTER, OF LA SALLE, NEW YORK, ASSIGNORS TO THE CARBORUNDUM COMPANY, 01 NIAGARA FALLS, NEW YORK, A CORPORATION OF PENNSYLVANIA REVERSIBLE AND IRREVERSIBLE THERMO PLASTIC BONDED ABRASIVE ARTICLES No Drawing.

of the bonding material and the abrasive grains used. During the grinding action the.

amount of work performed by the abrasive article is dependent on the ability of the article to clear itself, by which is meant the progressive exposure of fresh grinding surfaces, and incidentally, theremoval of the worn particles. In general, the types of materials which afford the qualities necessary in a satisfactory abrasiveare few and, consequently, the control of the grinding behavior to produce the desired results is obtained by selectlon proportioning and treating of the various onding agents. The various degrees and types of grinding action demanded in the art are obtained, for the most part,

by the choice and the amount of a proper bond suitable for the particular production demanded.

Abrasive articles are required to grind all sorts of material, both metallic and non-metallic, and the service demanded of them varies all the way from a very heavycutting action, such as the cleaning of fins and gates from castings, to very light work on hard tempered steel where very light, delicate cutting, known as finishing, is required, wherein it is desirable not to generate an excessive amount of heat. Such heat warps, checks and consequently destroys the material being ground. As .a result. many types of binding agents have been used with a relatively few types of abrasive material to produce the necessary characteristics required of any article for a given'purpose;

as A further preferable characteristic is that Application filed March 24, 1928. Serial No. 264,568.

an abrasive product contains a very large amount of abrasive grain in composition with a small amount of binder to afford adequate porosity. This feature is for the most part influenced by the fact that the abrasive particles themselves, rather than the bond, should be presented to the material being ground, in order that the proper cutting action may be obtained. Further, the use of a small amount of bond is more conducive to free cutting by the abrasive article.

By varying the amount of bond the characteristic WhlCll is known as grade, or resistance of the particles to removal from the composite mass, is obtained; in general, the more bond the harder is the grade. In obtaining adequate strength it is sometimes necessary to use a very tough 'bond. An alternative, as far as strength is concerned, is to use a large amount of bond, but this reacts against '0 e principle outlined above, namely, that of providing a porous, open structure composed of a relatively large amount of abrasive grain and a very small amount of binding agent.

Thus, in practice, some bonds lend themselves for use over only a small range of grades, whereas other bonds might be termed universal grade range bonds inasmuch as it is possible to produce articles with these varying from the hardest to the softest required in'practice. The latter type is relatively rare, however, and it is usual that each specific bond covers only a portion of the grade range, respectively.

These bonds may be classified into organlc and inorganic materials. The inorganic bonds are represented chiefly by ceramic materials such as various'types of clays or other earthy substances. Such bonds may represent ceramic articles of various degrees of vitrification including a completely fused glass-like condition. For certain other purposes, a porcelain type of bond may be used. A further type is one'made with water-glass or sodium silicate solution-and used either in either natural or artificial.

the condition of partial dehydration or one of complete fuslon. Such ceramic bonds may be composed of a single clay or more usually of a mixture of mineral ingredients.

In the fabrication of such ceramic articles, the molded article is usually matured by subjecting it to relatively high temperatures, in general between 800 and 2500 F. The bond usually undergoes an interaction and the heat treatment is prolonged for periods of from 6 to 14 days.

Under the classification of organic materials there are several types, such as shellac, glue, and rubber, and phenol-aldehyde synthetic resins, such as Redmanol.

In the case of glue the curing treatment consists essentially of a drying operation. The cure for shellac and synthetic resins includes a transformation of the material to a relatively infusible or thermo-irreversible condition. By this it is meant that reheating at the initial temperatures used in molding will not produce the same degree of plasticity.

Further, the bond undergoes a chemical change and consequently on cooling the comonents are not the same as existed originally.

11 rubber bonded articles the cure is brought about by means of vulcanization or the reaction of the rubber with a vulcanizing agent, such as sulphur. The resulting components are not the same as in the original mixture. For this reason they are classified as thermoirreversible bonds.

In the practice of our invention we propose to use other organic bonds. One group of these bonds is classified as reversible thermoplastic materials, by which it is meant that reheating renders the material plastic within a temperature range used in molding. The procedure for making an abrasive article with such a bond comprises merely moistening the abrasive grains with water or xylol or other wetting or plasticizing agent, mixing with bond, prexing in a mold while heated to a suit-able temperature between 200 and 400 F. to render the material plastic and adherent 'to the abrasive particles, cooling and removing the article from the mold in a completed form. No prolonged heat treatment is required as in the case of irreversible bonding agents. In addition to the above reversible thermo-plastic materials, we propose to use some of the irreversible'type and in particular some irreversible derivatives of %he reversible thermo-plastics mentioned be- The abrading material may be of any form, These may be classified further as aluminous, siliceous, or of the silicon carbide type.

The fused aluminum oxide abrasives are known under various trade names, such as Aloxite, Alundum, Alowalt, Borolon, etc.; those composed of silicon carbide are known as Carborundum, Cry'stolon,

Carbowalt, Electrolon, etc. Other kinds of abrasive particles known to the art maiy be used, such as corundum, emery, garnet, int, etc.

Bonding agents of the reversible type may contain rubber, rubber compounds, natural or synthetic resinous products, or other similar compounds. Some of these materials, together with their characteristics and molding temperatures, are here given.

1. Meta-styrene, a resinous pol mer of phenyl-ethylene is produced from t e liquid parent substance with the aid of heat or other suitable polymerization agent. The hard glassy resin lends itself readily to plastic molding, especially when used in a powdered condition and rendered plastic at approximately 350 F. The material is considerably ductile when heated and a thread can be pulled out to an extreme length. Bonded abrasive articles have tensile strengths of approximately 1200 lbs. per sq. in.

2. Pl'asticized or modified styrol may be made by any of the several methods. In neral, styrol may be compounded with rub er, gutta percha, balata, and other elastic gums. A preferred practice is to dissolve the rubber or gum'as gutta percha,balata, and the like, in the liquid styrol, phenyl-ethylene, and palmerize the solutions thus obtained.

For example, the gum, such as pale crepe rubber, vulcanized or unvulcanized, is dissolved or swollen in the pure styrol. Polymerization is then brought about, as by heating, to form a tough meta-styrol. After suitable heat treatment, a solid product results varying in properties'accordin to the quantity and quality of the gum ad ed. In general, the plasticizing gums may be added in amounts of 1 to 10% as desired. Bonded abrasive .articles made with modified styrol have shown tensile strengths of 1900 lbs. per sq. 1n.

Another example comprises the addition, to styrol, of a gum, such as rubber, in a. different solvent, such as xylene. This mixture is polymerized by treatment at approximately 275 F. for about 60 hours. The solvent may then be removed from the styrol rubber mixture by steam distillation or other suitable methods.

Where good adhesion is required between a pure styrol surface and another surface to which styrol will not adhere readily, this polymerized styrol-rubber-xylene solution may be used as a primin coating followed by a coating of styrol itself The resultant product of the plasticizing of styrol gives greater strength and shock resistance than the styrol alone.

By styrol it is understood that homologues are included.

3. Cellulose acetate, sometimes called pressmass powder, is obtained by the acetylation of cellulose and constitutes a thermo-plastic .per sq. in., in which is approximately the strength of the bond itself.

4. Various reaction products of rubber (vulcanized or unvulcanized) with the following materials may be used under this heading.

(a) Halogens, phenols and aldekydes when dried may be used as a molding composition at a temperature of 290-300 F., furnishing a product of a transverse tensile strength of approximately 7000 to 8000 lbs. per sq. in. Theproduct is apparently a compound of the ingredients used, rather than merely a mixture or combination of such.

(1)) Aldehydes alone or together with phenole if desired Rubber, preferably in solution, an aldehyde and a phenol together with a condensing agent are caused to react.

Specifically rubber, such as pale crepe, is dissolved in carbon tetrachloride, ooncen-i trated sulphuric acid added with thorough mlxing, and a formaldehyde solution then introduced. After a heat treatment at about 212 F. for two to three hours, a grayish white powder results. This material, when washed free from excessive ingredients and drled, comprises a brownish powder moldable at 140-160 C. and such a molded product ruptures at a tensile strength of about 400 lbs. per sq. in.

Other aldehydes may be used and, as stated above, phenols also may be brought into combination. A particular product, using rubber dissolved in carbon tetrachloride and sulphuric acid, together with formaldehyde,

molds at 300-340 F. and gives similar properties to those of the compositions including the phenols.

(0) Halogen alone, 01- iuzlogenated oompo'zmdso rboth in the form of a 10-20% solution of the powder in benzol or xylol. Such materials have good chemical resistance as to water, alkalies and acids, and yield tensile strengths of approximately 1000-1500 lbs. per sq. in.

Udntpoumds containing the sulphonyl (=S0 group Examples of such sulphonyl compounds are para-toluene-sulphonyl chloride, p-toluene sulphonic acid, para-phenol sulphonic acid.

By choosing suitable temperature conditions and reagents, themo-plastic products termed thermoprenes may be obtained varying in properties from tough materials, such as gutta percha and hard balata, to those of hard brittle shellac types. In making such a bond, the rubber is mixed with approximately 10% of its. weight of a sulphonyl compound, such as a sulphonyl chloride or a sulphonic acid as mentioned above and treated several hours at 250-27 5 F. The resultant products can be molded at temperatures from 200 to 350 F. i

A particular property possible with such sulphonyl rubber derivatives is one of good adhesion of bond to abrasive particles. With such We obtain a particular advantage in the structure of the abrasive article so produced. The bonding is of such a nature that sufliciently strong adhesion of grain and bond is obtained to allow an open structure prodnot of approximately 20% porosity in contrast to the dense product of about 4% oros-' ity obtained by present methods in or inary vulcanized hard rubber abrasive articles. In such wheels formed by present practice, the grain and rubber and sulphur are mixed on heated rolls resulting in a mass of grains embedded in the rubber bond with but little adhesion. The higher .porosities ossible with the thermo-plastic rubber derlvatives are obviously an advantage in grinding operations in that less heat is generated and a more eflicient clearing. action is obtained.

This adhesion is particularly trueof a bond made by treating 100 parts rubber with 7.5 parts of para-phenolsulphonic acid for about six hours at 285 F. This product can beused as a bond or an adhesive covering for the abrasive particles to promote adhesion to any other bonding agent. A particular thermoprene made with p-toluene sulphonic ..cid and sulphuric acid comprises a product which is more stable toward heat than rubber and this material may be used as a bond in applications where the temperature characteristics of rubber bonded articles are unfavorable.

It is possible to use these thermo-plastic materials in a vulcanized condition. Such vulcanization, however, converts them into irreversible or non-thermo-plastics, as described below.

(e) Phenols, together 'with a third material, either a halogen compound or sulphate An example of such comprising 100 parts rubber, -20 parts of phenol, such as cresol, and 10-20 parts of the third compound, such as rubber hydrochloride, is heated to 270320 F. for about twenty hours. The product is generally a hard thermo-plastic,which may be suitably homogenized. It is preferable that water soluble products should be removed.

5. Other thermo-plastic compounds of rubber or rubber derivatives may be used, such as 1 that obtained by heating rubber with 8 to grouping, can be vulcanized by a suitable heat treatmentwith sulphur. This converts them eventually into hard irreversible, non-thermo-plastics. An example of such a bonding agent is as follows:

Two parts of sulphur heated with 100 parts of thermoprene at about 280 F. for 15 hours converts it into an irreversible nonplast-ic product. By manipulating the sulphur content and the method of addition, the

softening temperature of the resultant product can be controlled and varied.

When such non-thermo plastics are used as an abrasive binder, the hardening, vulcanization or conversion from the reversible condition may be accomplished in situ by a suitable heat treatment after molding.

The bondin agents are used preferably in a finely divi ed condition. The abrading grains are preferably moistened by the addition of a wetting or plasticizing agent, such as water, xylol, etc. The abrasive material is mixed with the bonding agent until each abrading grain is sufliciently coated with the bonding agent. The mixture is then placed in a mold and subjected to a temperature suitable for the particular material somewhere between 230 -500 F. Such a temperature is csuflicient to cause the material to become sufficiently plastic to bond the abrading grains.

Particular compositions of abrading materials embodying our invention are given below.

Example 1.-Ten (10) parts of pulverized resinous meta-styrene of approximately 80 mesh are mixed with 90 parts of abrasive grains of 100 mesh. These materials are moistened with water, placed in a mold, pressed at 2000 lbs. per sq. in. while at 350 F., cooled to about 150 F. and removed from the mold in a completed form.

Example 2.-Ten (10) parts of a thermoplastic derivative of rubber such as the reaction roduct of rubber and para-toulene-suL PhOIllC acid ground to about 80 mesh are mixed with 90 parts of abrasive ains of 100 mesh. These materials are moistened with water, placed in a mold, pressed at 2000 lbs. per sq. in. while at about 260 F., cooled to about 150 F. and removed from the mold in a completed form.

Example 3.-Eight (8) parts of the thermolastic reaction product of vulcanized rub er, halogen, phenol, and aldehyde of about 80 mesh are mixed with 92 parts of abrasive grain of 100 mesh. These materials are moistened with water, placed in a. mold and pressed at 2000 lbs. per sq. in. while at about 260 F., cooled to about 150 F. and removed from the mold in a completed form.

Example l.-Ten (10) parts of a thermoprene-such as that obtained by treating a mixture of 100 parts of rubber with seven parts of p-toluene sulphonic acid and three parts of sulphuric acid for about 10 hours at 250 F.-are mixed with part of sulphur and 90 parts of abrasive grain of 100 mesh. These materials are moistened with water, molded and heat treated at 280 F. for 15 hours. This product represents an irreversible plastic bonded article.

Small quantities of sulphur ma be present in the rubber-derivative thermop astic mixes without causing conversion to non-thermo plastics providing the heat treatment is not toolong.

After molding the reversiblethermo-plastic roducts the abrasive material is in its finished state and does not require any prolonged or subsequent heat treatment to finish or cure it as is the case with abradmg materials made by former methods. On the other hand, the irreversible derivatives of the reversible plastics lproposed in our invention require, in genera a prolonged heat treatment after the molding operation.

It is understood that our invention may be otherwise embodied or practiced without departing from the scope of the appended claims.

We claim 1. A composition comprising abrasive grains and reaction product of vulcanized rubber, halogen, phenol and aldehyde.

2. A composition comprising abrasive grains and a bonding agent which when reheated becomes lastic within a temperature range correspon ing substantially to its initial shaping temperature.

3. In an abrasive material, a composition comprising particles of abrading material sive grain, then uniting the abrasive ains 80 material, the-step consisting 1n mixing abra- 100 2 the temperaureat which it was initially 115 and a thermally reversible binder therefor abrasive grains and the bonding a nt and that engages the grains by adhesion due to hardening the bonding agent by coo g. subjecting the material to a temperature such In testimony whereof we have hereunto set as to render the bonding agent sufliciently our hands. plastic to engage the abrading grains by an RAYMOND C. BENNER. l0 adhesive action. I GARNETT H. PORTER. 4. In an abrading material, a plurality of grains of abrading material and an organic bonding agent therefor and joined thereto 10/ while in a plastic state at a temperature in excess of 200 F.

5. In the method of forming an abrasive material, the steps consisting 1n forming a coating of a powdered binding agent on abraby subjecting them to a temperature s cient to cause adhesion between the abrasive agent and the bonding agent, and thereafter hardening the bondlng agent by cooling. 6. In'themethod of forming an abrasive material, the steps consisting in en plying abrasive material and a reversible onding' agent to a mold, subjecting the material in I the mold to a temperature in excess of 200 25 F., and hardening the bonding agent by 'coolmg. p

7 In the method of forming an abrasive material, the step consisting in mixing abrasive material with the reaction product of vulcanized rubber, halogen, phenol, and aldehyde in a pulverized condition and subject-' ing the mixture to pressure at a temperature in excess of 200 F. T

8. In the method of forming an abrasive sive material with the reaction product of vulcanized rubber, halogemphenol and aldehyde in a pulverized condition and subjecting it to a temperature at which the rubber 40 or rubber compound is rendered sufficiently plastic to adhere to the abrading material. 9. A composition comprising abrasive grains and reaction product ofa plasticizin agent, vulcanized rubber, halogen, phenol'an 1 45 aldehyde. 1 10. "-An abrading composition comprising 1 particles of an abradin substance a plasticizing agent, and a bOlHfillg agent that is rendered plastic when underuse at substantially formed.

11. In a abrasive material, a composition comprising particles of abrading material, a plasticizing agent, and a binder therefor 55 thatengages the grains by adhesion due to subjecting the material to a temperature such as to render the bonding agent sufiiciently plastic to engage the abrading grains by an adhesive action. 0 12. In the method of formin an abrasive 126 material, the steps consisting in forming a coating of a powdered binding'agent, and a. plasticizmg agent on abrasive grain, uniting the abrasive grains by subjecting them to a temperature for causing adhesion between the 

